This invention relates to dialysate preparation systems and more particularly to a system for supplying dialysate under pressure to a patient station or to multiple patient stations.
Concentrate and water have been mixed in batch tanks to form dialysate for hemodialysis. Manual mixing in batch tanks is subject to error by the preparer and it is difficult to maintain sanitary conditions. Systems for continuously mixing concentrate and water have been used. U.S. Pat. No. 3,441,136 and 3,508,656 -- Serfass et al. are examples of systems in which concentrate and water are continuously mixed for each individual patient.
The mixing can also be done continuously at a central location which supplies dialysate to a number of patient stations. "A central system for the continuous preparation and distribution of hemodialysis fluid," Grimsrud et al., Vol. X, Trans. Amer. Soc. Artif. Int. Organs, 1964, p. 107, describes such a central system. Dialysate must be supplied to each dialyzer at a constant pressure and at a temperature which is comfortable to the patient. In the aforesaid Grimsrud et al. system, a constant pressure is maintained by a head vessel. Further regulation is provided by a needle valve at each dialyzer. The temperature of the dialysate is controlled by two temperature controlled mixing valves at a central location.
The use of a central preparation system has advantageous of economy and reduced supervision in places such as a hospital where a number of patients are undergoing hemodialysis. There are two principal disadvantages of a central system. One disadvantage accompanies the use of a head vessel. The head vessels normally used in such systems are large and cumbersome. It is common to install such a vessel above the false ceiling of the hospital.
The use of a head vessel has the additional disadvantage of presenting a sanitation problem. Often, open vessels which are exposed to dust and bacteria in the air are used. Even closed head vessels have air pockets at the top thereof which expose the dialysate fluid to bacteria in the air. Often, head vessels have regions of little or no flow and in these regions, stagnant dialysate can become contaminated.
The other problem with prior central preparation systems arises because these systems heat the dialysate at the central location. A common dialysate temperature is not comfortable for all patients. Also, heating large quantities of dialysate at a central location requires high electrical power at that location and a special circuit must normally be installed to provide such power.